Pharmacokinetics of low molecular weight heparins in animal models.

Low molecular weight heparins (LMWHs) are a diverse group of depolymerized heparin preparations with molecular weights ranging from 1800 to 12,000 Da. Due to manufacturing differences, there are marked structural variations between LMWHs that exhibit distinct pharmacologic and biochemical profiles. Pharmacokinetic studies generally use indirect pharmacodynamic measures, particularly anti-Xa activity. Animal models have shown considerable variation between preparations in anti-Xa activity and other pharmacodynamic measures, including bioavailability and release of tissue factor pathway inhibitor (TFPI). Each LMWH has a specific, assay-dependent pharmacokinetic profile, reinforcing the concept that each LMWH is a distinct, noninterchangeable, pharmaceutical product.